I have the same problem, except in the right shoulder. Sometimes the pain can be almost unbearable, and it throbs nonstop.
I agree with the others about
heat; I will either use a heating pad or get in a really hot shower with the water focused on my shoulder.
I also have one of these:
www.amazon.com/Body-Back-10100000003-Buddy/dp/B0006VJ6TO It's called a Body Back Buddy. It's shaped like an "S," and I use it to work out knots/massage my own shoulder blades. Some days, that is the only thing that gives me any relief.
Hugs - Austen